Telephone circuits and apparatus



Nov. 27, 1928.

A. NYMAN Er AL TELEPHONE CIRCUITS AND APPARATUS Filed April 27, 1922 INVENTORS under Nymaa R 501i Conrol e w Y B WITNESSES:

A'TTORNEY I gerated.

Patented Nov. 27, 1928.

. UNITED STATES PATENT OFFICE.

ALExANnnn' NYMAN, or wmxrNsnuno, AND FRANK CONRAD, or PITTSBURGH,

rENNsYLvANIA, AssIoNonsro wnsrmenonsn nnncrmc AND mANUrAcrun- ING coMrAN A CORPORATION or PENNSYLVANIA.

TELEPHONE CIRCUITS AND APPARATUS.

Application filed April 27, 1922 Serial No. 556.834.

that the intensity of vibration of the diaphragm-is greatly increased over that corresponding to non-resonant frequencies. As "can readily be seen, such resonant efiectsare 20 especially undesirable when attempting to reproducesound waves from currents modulated in accordance with music, since the fre-.

quency corresponding to the resonant freof the diaphragm. is greatly exaglquency We have found, however, that, by operatively associating a combination of inductive and capacitive reactance elements with telephone translating apparatus of the aforementioned type, and by tuning-said reactance elements to the'resonant frequency of the apparatus, the'above mentioned undesirable e cots aresubstantially' eliminated. The

j'combination of inductive and capacitive re-- actance elements may take the form of a series-resonant or'av arallel-resonant circuit and is associated wit the telephone apparatus in a manner hereinafter described. Variable resistors may be associated with the reactance elements to admit of adjustments tending to cause the resonant 'efiect of the combination to exactly oppose the resonant effect of the telephone apparatus.

With these and other objects and applications in view, our invention further consists in the mode of operation and the details of circuit arrangement hereinafter described and illustrated in the accompanying drawing, wherein Figure 1 is a diagrammatic view of circuits and apparatus embodying our invention;

Fig. 2 is a view-showing an alternative arrangement of inductive and capacitive reactance elements embodying our invention connected in a cascade-connected vacuumtube system.

In the illustrated embodiment of our invent on shown in Fig. 1, a vacuum tube. 1 of the customary three-electrode type is shown as containing an anode 2, a grid 3 and a hot cathode 4. The input terminals 3 and .4 there of may beconnected by conductors 5 and 6, respectively, to a source of energy (not shown) or to another vacuum tube 7, as shown in Fig. 2, to form a cascade-circuit connection.

A plate-filament circuit. 8- for, the tube 1 comprises a source 9 of direct-current energy, a telephone translating devicell and a tuned circuit 12. The telephone translating device 11 may be of any approved design and comprises a vibratory-element (not shown), preferably of such design as to have one resonant frequency only.

The tuned circuit 12' comprises the parallelconnected branches 13 and 14. A condenser 15 and a resistor 16 are connected in seriescircuit relation in the branch circuit 13 while an inductor 17 and a resistor 18 are connected vin series-circuit relation in the branch 14.

The magnitudes of the inductor 17 condenser 15 and resistors 16 and..18 are such as to cause the tuned circuit 12 to have a resonance curve which is exactly opposite to the resonance curve of the vibratory element embodied in the telephone translating device 11.

- When the currents traversing the platefilament circuit 8 are non-resonant to the resonant-frequency of the tuned circuit 12, the impedance of the circuit 12 to such currents is a minimum and the operation of the system is substantially unaflected'by the presence of tion of the device 11 to be independent of the frequency f of the energizing currents supplied thereto. v

In Fig. 2 is shown a 'ortion of the circuit arran ement of a stan ardized receiving set emb ying my invention, which, in practice,

has given highly satisfactory results. The

.fresistor-coupling device 19. An additional difference resides in the employment of seriesresonant circuits 21 and 38 in place of the parallel-resonant circuit 12 of Fig. 1.

The additional tube 7 is of the well known three-electrode type and contains an anode 22, a grid 23 and a cathode 24, the input electrodes .23 and 24 thereofbeing connected, by conductors 25 and 26 to a source of energy (not shown). A plate-filament circuit 27 of the tube 7 comprises the resistance coupling device 19 and the source 9 of direct-current energy which is common to both tubes. A grid conductor 29 of the tube 1 is connected, through a grid biasing condenser 31, to one terminal 32 of the resistor 19 while a filament conductor 33 of the tube 1 is connected, through the energy source 9, to the other terminal 34 of the resistor 19 to form a cascadeconnected circuit arrangement, as shown in Fig. 2.

The by-pass or series-resonant circuit 21 is connected in shunt relation to the resistor 19 and includes a condenser 35, an inductor 36 and a variable resistor 37 The magnitudes of the resistor 37, inductor 36 and condenser are such as to cause the tuned circuit 21 to have a resonance curve which issimilar to that of the natural period of vibration of the vibratory element embodied in the telephone translating'apparatus 11.

When the currents traversing the platefilament circuit 27 are non-resonant to the resonant-frequency of the tuned circuit 21, the impedance of the circuit 21 is a maximum, and normal energizing currents are supplied to the translating device 11. When the frequency of the currents, however, is caused to gradually approach the resonant frequency of the diaphragm embodied in the translating device 11, the impedance of the circuit 21 is correspondingly decreased. Hence, it can be seen that, as in the circuit arrangement of Fig. 1, the tendency for increases in the inten- Sity of vibration of the diaphragm of the translating device 11 is counteracted by corresponding decreases in the power-supplied thereto, thereby causing the operation of the device 11 to be independent of the frequency of the energizing currents sup lied thereto.

' If the vibratory element of the telephone translating device 11 is of such design as to have more than one resonant frequency, it is apparent that the undesirable effects of the additional resonant frequency maybe eliminated, or, at least, greatly reduced, by the provision of additional circuits connected as shown in Figs. 1 and 2 andtuned to said unde- I s'irable frequencies. By way of illustration,

assuming the translating device 11 to have two resonant frequencies, distortionless reception may be obtained by paralleling with the resonant circuit 21, wh1ch is tuned to one of said frequencies, a second resonant circuit 38 which is tuned to the other of said frequencies. I

While we have described certain forms of our invention in detail and while We have pointed out certain of the most obvious principles thereof, we do not intend that the language employed in the following claims shall be limited to the precise features described but intend that the claims shall be construed to cover all combinations which are fairly included in the language thereof when read in details and functions mentioned in the description or illustrated in the drawings.

We claim as our invention:

1. In an electrical system, telephone translating apparatus embodying a vibratory element having a resonant frequency, and a pair of parallel-connected circuits, one circuit ineluding,acapacitive-reactance element and a resistor, the other circuit including an inductive-reactance element and a resistor, said circuit constituting a parallel-resonant circuit tuned to the resonant frequency of said vibratory element and operatively associated with said apparatus in such manner as to admit of' variations in the energy supplied to said apparatus in accordance with variations in the frequency thereof, the value of said resistors being sueh as to cause the resonance curve of said parallel-resonant circuit to substantially conform to that of the said vibratory element.

- 2. The combination with a telephone circuit, of a sound-wave translating device for interchanging energy between said circuit and sound waves, said device embodying a vibratory element having a natural frequency-of vibration whereby the ratio of the interchange of energy is largelyincreased at frefrequencies approximating said natural frequency in accordance with a resonance curve, and. a parallel-resonant circuit serially included in said telephone circuit, said parallelresonant eircuit'comprising parallel-connected paths having inductive and capacitive reactances and resistances such as to produce a i resonance curve substantially corresponding, in tuning and in sharpness of tuning, to the resonance curve of said sound-wave translating device, whereby the amplitudes of an electrical quantity insaid telephone circuit and the amplitudes of the corresponding sound waves are substantially proportional for all frequencies within the range of the apparatus.

In testimony whereof, we havehereunto subscribed our names this 18th day of April, 1922. e

ALEXANDER NYMAN. FRANK CONRAD. 

